One example of conventional recognition systems is described in Japanese Unexamined Patent Application Publication (JP-A) No. Hei 6-314339 (Prior Art Document 1). This conventional recognition system detects a straight line as a specific pattern from an image as object data. The conventional recognition system can suppress a phenomenon that a false straight-line component appears around a true straight-line component, which has generally been a problem when using the Hough transform.
As shown in FIG. 1, this conventional recognition system comprises an image pickup section 31, an edge detecting section 32, a Hough transform processing section 33, a Hough space producing section 34, and a straight-line component extracting section 35.
The conventional recognition system having such a structure operates as follows.
That is, an image to be a recognition object is input from the image pickup section 31. Then, the image sent from the image pickup section 31 is differentiated by the edge detecting section 32, thereby edges of the image are detected. Then, a sequence of points representing each of the detected edges of the image are Hough-transformed by the Hough transform processing section 33. Then, a histogram according to Hough-transform function values (hereinafter this will be referred to as a Hough space) is produced by the Hough space producing section 34.
Finally, the straight-line component extracting section 35 detects frequency peak points in the Hough space, judges that the sequence of points of the edge of the image corresponding to Hough function curves passing through each of the detected peak points form a straight line, and extracts straight-line components from the image.
Herein, the operation of the straight-line component extracting section 35 will be described. The straight-line component extracting section 35 detects a maximum peak point in the Hough space produced by the Hough space producing section 34, extracts a straight-line component corresponding to the maximum peak point, and then derives a range and a contribution amount in which the maximum peak point exerts an influence on a frequency distribution of the histogram.
Then, according to the derived contribution amount in the above range, the straight-line component extracting section 35 corrects frequencies of the other peak points in the Hough space so as to suppress the influence of the maximum peak point.
Then, using the partially corrected Hough space, the straight-line component extracting section 35 detects the next larger peak point, extracts a straight-line component corresponding to that peak point, and subsequently performs the same processing in sequence.